rpmb_dev.wv.system.rc: change storageproxyd_wv_system stage

Changed boot stage at which storageproxyd_wv_system starts to
match the widevine launcher rc stage.

Bug: 371777025
Test: lunch qemu_trusty_arm64-trunk_staging-userdebug
Change-Id: I672a53b00df78b461309d6da0abd03d694475f10